1. Field of the Invention
This invention relates to a spray coating powder material having excellent high-temperature corrosion resistance and hence suitable for use with moving and stationary blades of gas turbines, as well as high-temperature components coated therewith. Moreover, it also relates to a spray coating powder material having excellent high-temperature corrosion resistance and hence suitable for use with burner diffusers and other components for boilers, as well as high-temperature components coated therewith.
2. Description of the Related Art
Recently, the development of gas turbines using a low-quality fuel oil as fuel is being carried on from the viewpoint of resources saving, fuel cost reduction and the like. However, such low-quality fuel oils contain large amounts of constituents accelerating the corrosion of metals, such as sulfur, vanadium and sodium, so that moving and stationary blades which are high-temperature components of gas turbines are exposed to a very severe corrosive environment. In such an environment, base metals comprising conventional heat-resisting alloys and heat-resisting steel fail to show sufficient corrosion resistance and hence undergo accelerated deterioration with time. In the existing state of the art, therefore, the corrosion resistance of base metals comprising heat-resisting alloys and heat-resisting steel is secured by coating them with a powder material to a thickness of about 100-400 .mu.m according to a plasma spraying technique. The power materials conventionally used for this purpose include, for example, Ni-50% Cr and MCrAlY materials (in which M represents Co, Ni, Fe or the like). that have been evaluated to have excellent corrosion resistance.
More recently, cruder low-quality fuel oils [for example, fuel oil C containing 10 to 30 mg/kg of sodium (Na), potassium (K) and vanadium (V)] have come to be used with a view to achieving a further reduction in fuel cost, and this exposes metallic components to a more corrosive environment. However, the aforesaid conventional Ni-50% Cr and MCrAlY materials fail to provide sufficient corrosion resistance and thereby function as a protective coating satisfactorily, so that the gas turbine shows a reduction in performance.
Under such circumstances, there is a demand for a spray coating powder material which can yield a sprayed coating having more excellent corrosion resistance and thermal shock resistance at high temperatures than those formed from conventional materials such as Ni-50% Cr and MCrAlY materials.